Electric discharge tube with anode cooling means



P. H. CLAY Oct. 5, 1954 ELECTRIC DISCHARGE TUBEWITH ANODE COOLING MEANS Original 'Filed Oct. 21, 1946 iiiiii.

r l k INVENTOR. PIEHRIIAJO CLAYDECEASED JORISDANIZZIIHJUGIEKYAMII/IWMR ATTORNEY Patented Oct. 5, 1954 UNITED STATS PATENT OFFICE ELECTRIC DISCHARGE TUBE WITH ANODE COOLING MEANS Pieter Hajo Clay, deceased, late of Eindhoven,

Netherlands, by Joris Daniel Heijligers, administrator, Eindhoven, Netherlands, assignor to Hartford National Bank and Trust Company,

as trustee Section 1, Public Law 690, August 8, 1946 Patent expires August 7, 1965 2 Claims.

This application is a division of a co-pending application, Serial No. 704,691, filed October 21, 1946, now U. S. Patent 2,535,669, issued December 26, 1950.

Various constructions of electric discharge tubes having a cylindrical cooled wall or wall portion are known. As a rule, these are electric discharge tubes of high power in which the anode is cooled. It has been proposed to provide such anodes with cooling fins. It has been found in practice that, in order to obtain the cooling desired, it is necessary to give these cooling fins comparatively large surface areas. This involves that the fins or ribs have a considerable length in a radial direction. Apart from the large space occupied by the whole construction and its considerable weight, another drawback is that a material temperature drop occurs in the fins and further, due to the large size, a high electrical capacity ensues which is highly undesirable.

In order to economize in weight, attempts have been made to make the fins of aluminium instead of copper which is to be considered as the most suitable material because of its high thermal conductivity. In this case, a saving in weight is obtained, but since aluminium has a lower heat conductivity than copper, the temperature drop in the fins increases, due to which the cooling becomes less eiiective.

In the form of construction according to the present invention all of the said drawbacks are obviated. Shorter fins suffice, with the result that the drop of temperature is smaller and the whole construction becomes so much less voluminous that even with the use of copper, a relatively small weight is attained. Owing to the small drop in temperature the load of the part to be cooled, for example an anode, may be high. Moreover, the electrical capacity of the anode provided with a cooler according to the present invention becomes materially lower as compared to the well-known constructions owing to the smaller size of the former.

Finally, the construction according to the invention may be used for anodes having a considerable length. This is not the case with the conventional constructions.

When using cooling fins extending in an axial direction, the construction according to the present invention has some further advantages over the conventional constructions. Owing to the smaller size the total thermal conductivity in an axial direction of the whole system of the anode cooler is lower than in the constructions hitherto used. The great advantage is that at the anode end, where the dissipation is low, the temperature is materially lower than at the area where the dissipation is a maximum. In discharge tubes having a glass envelope and metal anode the metal-to-glass seal has, in general a minimum dissipation, with the result that this area, in the form of construction according to the invention, has a lower temperature than the other parts of the anode, owing to which on the one hand the risk of cracking, leaks or the like is highly reduced and on the other hand operation at a higher anode temperature is possible without incurring the risk of the metal-to-glass seal becoming too hot.

The electric discharge tube according to the invention exhibits the feature that in the immediate vicinity of the wall to be cooled there are means to bring a cooling medium through a certain number of parallel-connected paths, each having a length or" at most of one of the dimensions of this wall, in intimate contact with this wall or with heat exchanging means on this wall, the surface part of this wall, where the medium is in intimate contact with this wall or with heat exchanging means on this wall,

amounting to at least half the total surface area" of the said wall.

As a rule, the said paths will have a maximum length of of the smallest dimension of the wall portion to be cooled. Sometimes however, for example when the two dimensions (diameter and height) of the wall to be cooled are much the same, the length of these paths for the medium may be chosen to exceed one-third of the smaller dimension of the wall, but smaller than one-third of the larger dimension of the wall, without any deleterious effect with respect to the resistance of flow of the medium. The length of the paths for the medium may, as an alternative, be given the last-mentioned value if the viscosity of the medium has a very low value. If the medium, during the cooling of the wall or the wall portion intimately contacts only or substantially with the heat exchanging means on the wall and consequently not with the wall itself, the surface of the wall portion which is provided with these means amounts at least to half the total surface of the wall.

To reduce the resistance experienced by the medium, the exchanger according to the invention comprises a large number of short parallelconnected gas ducts. As a result thereof, the speeds of the gas are small which is contributive to the exchange of heat. To prevent the current of heat from attaining an undue value per surface unit, in designing the heat exchanger according to the invention, we proceed in a manner such that, over at least half the surface area of the cylindrical wall, the medium is in intimate contact with the wall or heat-exchanging means on this wall. The wall, with which the medium is in heat-exchanging contact, may either be smooth or, as has already been stated, comprise heat-exchanging means which may, for instance, consist of projecting parts such as ridges. Ridges for increasing the transfer of heat are known per se. Owing to the excellent properties of the heat exchanger according to the invention, however, the projecting parts may be shorter than with the conventional constructions. Apart from the advantage of saving material, thus obtained in general, the additional advantage is secured that the capacity of the metal parts of the discharge tube is much smaller than in the case of using the hitherto known constructions.

In definite cases, when proceeding according to the present invention, the usual liquid cooling, which usually involves numerous complications, may be replaced by cooling by means of gas e. g. an.

According to the invention the parallel-connected paths for the cooling medium along the wall portion of the tube to be cooled or along the heat exchanging means on this portion of the tube may extend substantially at right angles to the axis of the tube. structurally this may, for instance, be effected by providing on the portion of the tube to be cooled, a number of annular plates which are spaced apart from one another. As an alternative one or more metal strips may be wound edge-on around this portion of the tube and fastened thereto. In order to form the channel systems in these constructions a number of preferably triangular partitions extending substantially parallel with the axis of the tube may, according to the invention, be fitted against the outer walls of the members forming on the tube the parallel-connected paths for the medium, the said partitions cooperating with other partitions in such a manner as to form a number of channels for the supply of the cooling medium and a number of channels for the outlet thereof. The tube with the partitions may be connected to a supply and an outlet duct for the cooling medium. In such a case, a fan causes the cooling medium to flow along the portion of the tube to be cooled. As a rule it is more efiicient to place the fan in a delivery pipe (and consequently not in a suction pipe), because the volume of the cold cooling medium, which has consequently not yet been heated by the heat given ofi by the tube, is much smaller than the volume of the cooling medium heated by the tube.

The partitions which consequently, according to the last-mentioned embodiment of the invention, may extend substantially parallel with the axis of the cooled portion of the tube may then be shaped as an isosceles triangle and are positioned in such a manner with respect to the axis 4 of the tube, that the bisector of the vertical angle of this triangle intersects the axis of the tube perpendicularly. This shape of the partitions generally permits a very small surface area of the partitions, as result of which the tube comprising such a cooling system has a low electrical capacity. For this reason this construction is particularly suitable to make the partitions and the portion of the tube to be cooled form a constructional unit. In this case the partitions are usually made from metal.

If a discharge tube, in which the wall portion to be cooled is very large, has to be equipped with two systems of channels for the supply or outlet of the cooling medium, as has been set out above, it is advisable, according to a further embodiment of the invention, to connect two of such channelsystems to a common supply or outlet pipe, this pipe surrounding the tube as a cylindrical casmg.

It has still to be pointed out that the cooling system, according to the present invention, is not only suitable for cooling transmitting tubes but also for X-ray tubes, rectifying tubes and so on, in short whenever a discharge tube has to be cooled intensively.

In order that the invention may be clearly understood and readily carried into effect, it will now be described more fully with reference to the accompanying drawing.

Fig. 1 is a vertical cross-section of an electric discharge tube and anode cooling means therefor in accordance with the invention;

Fig. 2 is a cross-sectional View of Fig. 1 taken along lines 2-2 Fig. 3 is a vertical cross-section of a modification of the device shown in Fig. 1.

In the construction shown in Figs. 1 and 2, the paths through which the cooling medium contacts with the parts of the tube to be cooled are very short. The anode 50 to be cooled is furnished with a large number of rings 5i that are spaced apart from one another. To the outer edge of these rings are secured triangular partitions 52 which are shown in side view in Fig. 1. These partitions form a certain number of radial ducts about the anode. They are alternately closed at the top 53 or at the bottom 54. In Fig. 2, the ducts closed at the top are shaded. The ducts which are open at the top serve for the supply of air. The cooling air, upon entering the space between two rings 51, moves in a radial direction as shown in Fig. 2, and enters the space between two partitions, which is closed at the top but communicates at the bottom with the outlet duct 55, in which is maintained a sub-atmospheric pressure by means of a fan.

The construction shown in Fig. 3, in which the anode 60 to be cooled is very long, comprises two parallel-connected systems of ducts for the outlet of the cooling air, viz., one between first partitions 6| and one between first partitions 62. Similarly to Fig. 1, the spaces between the partitions GI and the spaces between the partitions 62 are alternately closed by other second partitions at the top and the bottom. The spaces between the partitions 6|, which are open at the bottom and the spaces between the partitions 62 which are open at the top, communicate with an outlet duct 63 in common which, at the tube, surrounds it as a cylindrical case 68. Owing to the fact that the partitions SI and 62 are shaped as an isosceles triangle of which the bisector of the vertical angle cuts the axis of the anode perpendicularly, the partitions BI and 62 may be given a small radial dimension, which is advantageous in conjunction with reducing the electrical capacity of th tube as much as possible which is due to the presence of the said metal partitions. As shown in the drawing, the base of the triangular partitions 6i and E2 is parallel to the longitudinal axis of the tube, and the second closing partitions are secured to the legs of those triangular partitions.

The electrical discharge tube shown in the accompanying drawing comprises an anode Bil which is relatively long in proportion to its width. Extending radially outward from the anode are a plurality of cooling fins 65 which are arranged so that a cooling medium such as air is directed and flows over the fins and cools the latter.

The cooling medium is directed over the fins by a plurality of ducts formed by partitions each constituted by two sections 6| and 62 disposed radially along the peripheral edges of the fins and forming with the fins peripheral spaces around the anode and fins which serve as supply and inlet passages for a cooling medium. Each section of the partition has the shape of an isosceles triangle whose base is parallel to the longitudinal axis of the anode. Alternate pairs of these triangular members are closed ofi at opposite ends of the partition to form a series of inlet ducts, while adjacent alternating partitions of the tube members are closed off at the junction of the triangular member to form a series of exhaust ducts which communicate with a common exhaust duct 63 in a cylindrical casing 64 surrounding the anode.

The triangular member should, preferably, have a small radial dimension in order to reduce the electrostatic capacitance created by the metallic fins and partitions surrounding the anode.

What is claimed is:

1. An electric discharge tube comprising 2. cylindrical anode having a given longitudinal axis and means for cooling of the anode by heat exchange with an external cooling medium, said cooling means comprising a plurality of metallic radial fins secured to the outer surface of the anode, a plurality of first partitions disposed radially along the outer edges of the fins in spaced apart rows of two aligned partitions, each of said partitions having the Shape of an isosceles triangle the base of which extends parallel to the longitudinal axis of the anode, each pair of radially adjacent partitions defining a space therebetween, a plurality of second partitions each secured to the legs of adjacent ones of said first partitions and alternately closing off at top and bottom the spaces between adjacent ones of said first partitions, and a cylindrical case surrounding the partitions and defining with the spaces between the first partitions, with which the case communicates, an outlet duct for the cooling medium.

2. An electric discharge tube as claimed in claim 1 in which the cylindrical case is joined to the partitions at the apices of the triangular partitions opposite the base, and in which an exhaust duct communicates with the interior of said case.

References Cited in the file of this patent UNITED STATES PATENTS I Number Name Date 2,406,121 Young Aug. 20, 1946 2,406,551 Lucke Aug. 27, 1946 FOREIGN PATENTS Number Country Date 514,651 Great Britain Nov. 14, 1939 

